How do I Change the Player gravity (run trough the ceiling)

I cant find out how to make my caracter running to the top.

The flow is:

Project runner, runnig to right.

-While running press jump

-In the air change the character's gravity

-The character will be running through the ceiling now

-While running through the ceiling press jump again

-In the air the characters gravity should change so he will run trough the bottom now

I already try Platform.Gravity = Platform.Gravity * -1, but the behavior is weird, it just doesn't work as expected.

What you are looking for is Angle of Gravity. Set it to 270degrees to go up. Then set it to 90 to go down. You'll also have to flip your sprite as well.

platformer |set world gravity = world gravity * -1

does not works?

Set Platform Gravity to -1000